The present invention relates to pneumatic brake systems, and, more specifically, to control valves used in such systems and electronic switches to activate the control valves.
The majority of current heavy vehicle brake systems use compressed air to apply the brakes. Control signals are transmitted from the driver of the vehicle to the control valves of the brake system, and the brakes are applied. Brakes are generally divided into two categories, service brakes and parking brakes. Service brakes are used primarily to slow the vehicle to a stop when the vehicle is moving. Parking brakes are used primarily for helping to prevent the vehicle from moving from a parked position, and may also be used in an emergency situation to slow a moving vehicle when the service brakes have failed to provide a redundant brake circuit.
For service brakes, an operator generally depresses a brake pedal, which in turn actuates a control valve, allowing air pressure to travel to the brake, and the brake is applied. The parking brake is generally engaged by a vehicle operator by actuating a push/pull hand lever within the cab of the vehicle, located on the vehicle dash. The parking brake is generally a spring brake which is normally engaged, meaning that air pressure must be applied to the parking brake in order to release it. Thus, when there is no air pressure present, the parking brake is applied. Accordingly, if a vehicle loses air pressure (i.e., ruptured hose, failed component, etc.), and thus loses service brake airpressure (e.g.,  less than 30-35 psi) and the ability to apply the service brakes, the parking brake will automatically engage, and act to slow a moving vehicle. Likewise, when the vehicle is parked and/or not in use, the parking brake can be engaged by the operator, helping to prevent the vehicle from moving from a parked position.
As mentioned above, typical current day heavy vehicles have a push/pull knob located in the cab of the vehicle which is used to engage and disengage the parking brake. A vehicle may have more than one push/pull knob, depending upon whether there is an additional control for the parking brakes on a trailer attached to the vehicle. The push/pull knob is generally connected to a control valve, which controls the flow of air to the parking brake. Generally, when an operator pushes the valve in, it acts to provide air pressure to the parking brake, and thus release the brake, allowing the vehicle to move. In order to apply the brake, the operator pulls the push/pull knob, thus removing air pressure from the parking brake and causing it to engage. When the knob is pushed in, the air pressure acts to engage the knob and keep it in the pushed in position. Such push/pull knobs also have a feature which allows a manual override where, even if there is a failure in the air system, or the air pressure is not high enough to engage the push/pull knob, the operator may manually hold the knob in to disengage the parking brake and move the vehicle a short distance.
While this is a relatively simple system, it can have disadvantages. For example, because air lines are routed to and from the switch in the dash of the vehicle, the dash must be relatively large, to accommodate the air hoses. Additionally, it can be difficult to install the valve and associated air hoses, because of the tight area in which they go behind the dash. Furthermore, maintenance can be difficult in a case where there is an air leak in the valve or associated hoses. The air leak can be difficult to find and repair due to the restricted area of the dash.
In accordance with the present invention, an apparatus for controlling at least one park brake in a vehicle is provided. The apparatus includes an electric switch assembly, which can, but need not, have at least portions that are mounted in the vehicle dash. The electric switch assembly can be manually controlled between first and second positions by the vehicle operator including related to controlling a park brake function. A pressure switch subassembly communicates with the electric switch assembly. The pressure switch subassembly has a first state and a second state. The pressure switch subassembly can be in the first state when at least a threshold pressure is detected and can be in the second state when less than the threshold pressure is detected. The apparatus includes a brake release actuating subsystem including at least one park brake release actuator. The apparatus also includes a control assembly in communication with each of the electric switch assembly and pressure switch subassembly that controls the application of fluid to the at least one park brake release actuator.
The electric switch assembly can be a solenoid actuator assembly that includes a solenoid actuator push/pull knob and switch contacts. The solenoid actuator push/pull knob is in a first position and the switch contacts are in a first state when the park brake is released and the solenoid actuator push/pull knob is in a second position and the switch contacts are in a second state when the park brake is applied. The solenoid actuator push/pull knob can be in the second position when less than the threshold pressure is detected by the pressure switch subassembly. The solenoid actuator assembly can include a return spring for use in providing the solenoid actuator push/pull knob in the second position.
The control assembly can also include a solenoid pilot valve subassembly and an electrical conductor connected between the electric switch assembly and the solenoid pilot valve subassembly and in which electrical power is supplied to the solenoid pilot valve subassembly using the electrical conductor. The control apparatus can include a relay valve subassembly in fluid communication with the solenoid pilot valve subassembly and which the relay valve subassembly is also in fluid communication with the pressure switch subassembly. The relay valve subassembly can include an output applied to the at least one park brake release actuator.
A vehicle having the apparatus including the control assembly can include at least one park brake fluid carrying line and an electrical conductor connected to the electric switch assembly. The electrical conductor can originate from the vehicle dash or the vehicle cab. The at least one park brake fluid carrying line can be located away from the vehicle dash or the vehicle cab and on the vehicle chassis. One or both of the vehicle cab and the vehicle dash can be free of any fluid carrying line used by the apparatus.
The present invention also provides a method for controlling at least one park brake system in a vehicle. The method includes providing an apparatus that includes an electrical switch assembly and a pressure switch subassembly in communication with the electric switch assembly. The pressure switch assembly detects whether a threshold pressure exists related to a fluid system of the vehicle. The electric switch assembly can be changed between a first position and a second position, depending on the threshold pressure, to release the at least one park brake system.
The park brake system can be applied when the pressure switch subassembly detects a pressure less than the threshold pressure. The park brake system could be applied by causing the electric switch assembly to change to the second position. The apparatus can include a pilot solenoid valve subassembly that de-energizes when the electric switch assembly is in the second position. The pilot solenoid valve subassembly might fluidly communicate with a relay valve subassembly and the relay valve subassembly can be used to interrupt fluid delivery to the park brake system.
The electric switch assembly can be manually controlled while the pressure switch subassembly is detecting a pressure greater than the threshold pressure. The park brake could also be released by manually controlling the electric switch assembly when the pressure switch subassembly detects a pressure less than the threshold pressure.
All fluid associated with the apparatus can be located away from the vehicle dash. At least portions of the electric switch assembly could be mounted to the vehicle dash. The electric switch assembly, in such a case, includes at least a first electrical conductor that extends from the vehicle dash.
Based on the foregoing, several advantages of the present invention are readily seen. The method and apparatus provide the ability to locate all fluid carrying lines away from the vehicle dash and/or inside the vehicle cab, thus allowing for easier installation and maintenance of the operator actuated electric switch. Additionally, the vehicle dash may be smaller due to not having to locate fluid lines behind the dash. Furthermore, the invention can include a unique combination of electric switch, pressure switch and control for desired automation or semi-automatic operations.
Additional advantages will be seen when reading the following description of the invention, particularly when taken in conjunction with the accompanying drawings.